The present invention relates generally to welding machines and, more particularly, to a method and apparatus for remotely controlling operation of a power source of a welding-type system through the transmission of control signals across a weld cable.
MIG welding, formerly known as Gas Metal Arc Welding (GMAW), combines the techniques and advantages of TIG welding's inert gas shielding with a continuous, consumable wire electrode. An electrical arc is created between the continuous, consumable wire electrode and a workpiece. As such, the consumable wire functions as the electrode in the weld circuit as well as the source of filler metal. MIG welding is a relatively simple process that allows an operator to concentrate on arc control. MIG welding may be used to weld most commercial metals and alloys including steel, aluminum, and stainless steel. Moreover, the travel speed and the deposition rates in MIG welding may be much higher than those typically associated with either Gas Tungsten Arc Welding (TIG) or Shielded Metal Arc Welding (stick) thereby making MIG welding a more efficient welding process. Additionally, by continuously feeding the consumable wire to the weld, electrode changing is minimized and as such, weld effects caused by interruptions in the welding process are reduced. The MIG welding process also produces very little or no slag, the arc and weld pool are clearly visible during welding, and post-weld clean-up is typically minimized. Another advantage of MIG welding is that it can be done in most positions which can be an asset for manufacturing and repair work where vertical or overhead welding may be required.
A wire feeder is operationally connected to the power source and is designed to deliver consumable wire to a weld. To further enhance the operability of the wire feeder of a MIG welding system, known welding systems have connected the power source and the wire feeder to one another across a dedicated control cable that is in addition to a dedicated weld cable such that control signals defining the operational parameters of the power source are transmitted or fed back from the wire feeder to the power source, generally referred to as remote control.
One type of remote control device is used to regulate the operational welding parameters, and switch the welding power source output ON and OFF as well as change the power source mode via a pendant that connects to the power source by a multi-conductor cable. The solution is schematically illustrated in FIG. 1A. A wire feeder 2A is connected to a power source 4A by a control cable 6A that includes a 14-pin connector. The cable 6A used to transmit operational information to, and in some cases, from the power source may incorporate 2 to 14 conductors depending on how many functions are to be controlled. Separately connected between the power source 4A and wire feeder 2A is a high voltage weld cable 8A that delivers welding power to the wire feeder and creates a voltage potential between an electrode and a workpiece.
A significant drawback to this control cable-based scheme is that the control cable is typically fragile relative to the welding cables designed to carry high currents at high voltages. Welding machines are commonly used at construction sites or shipyards where it is not uncommon for the welding machines to be periodically relocated or surrounded by other mobile heavy equipment operating in the same area. As such, the remote control cable can become damaged by being crushed or snagged from contact with surrounding machines and/or traffic. This can cause damage to the wire feeder and/or the welding power source if internal power conductors become shorted to signal leads that are connected to sensitive signal level circuitry.
Referring now to FIG. 1B, another remote controlled system includes a radio transmitter type remote control. This approach has several disadvantages. First, electric arc welding can create radio frequency interference that negatively affects the communication between a transceiver 9A of the wire feeder 2B and the transceiver 9B of the power source 4B. Second, if the system is used inside metal structures such as tanks, ships, or large aircraft, the radio link can be lost due to the shielding effect of the metallic surroundings. Third, if multiple welding stations use a radio link for remote control, each control loop would require a separate security code to prevent cross-talk or mis-transmission of control signals to the wrong welding machine.
Another remote control solution is described in U.S. Ser. No. 10/604,482, which is assigned to the Assignee of the present application. Notwithstanding the numerous advancements achieved with the invention of the aforementioned pending application, such a system relies upon pulse width modulation to remotely transmit operational data from a wire feeder to a power source across a weld cable. By using pulse width modulated signals to remotely control operation of a power source, the amount of data as well as variability in the types of data that could be transmitted between the wire feeder and a power source is limited when compared to that which may be achieved with serialized or encoded communications. Further, with the system described in the aforementioned pending application, the wire feeder is constructed without a contactor and thus requires an internal DC power supply to power the electronics of the wire feeder. That is, the invention of the above-referenced application teaches the avoidance of an open circuit voltage (OCV) between the wire feeder and power source. As a result, absent a DC power supply, the wire feeder cannot be minimally powered so as to communicate with the power source to initiate the welding process.
It is therefore desirable to design a remote controlled welding machine that receives command signals from a wire feeder across a weld cable to control or otherwise regulate operation of a power source. It would also be desirable to design a remote controlled welding system having with a battery-less wire feeder whereupon electronics of the wire feeder are powered in a conventional manner, but the OCV between the wire feeder and power source is used as the backbone of a communications link between the wire feeder and power source for the transmission of control commands.